This invention relates to a device for the agile steering of a light beam and more particularly to a complementary pair of mechanically driven phased array-like elements which steer light into a desired diffraction order.
The steering of a collimated laser beam is a fundamental building block for many optical systems. Common examples include bar code scanners, laser radars, laser machining applications and laser printers. Traditionally, this function has been limited to systematic scanning and has been accomplished by mirrors or holographic scanners.
Recent developments in microoptics and particularly in binary optics, however, has led to the possibility of quick non-systematic scanning as binary optics technology is capable of manufacturing large arrays of optically coherent microoptics. The use of a complementary pair of binary optics microlens arrays for agile steering a laser beam was published by Goltsos and Holz in Opt. Eng. 29 (1990). A binary optics microlens array, however, has high losses in diffraction efficiency and diffraction leakage into many neighboring orders. The use of a phased grating profile for beam steering also has been disclosed in U.S. Pat. No. 4,585,307. This patent teaches a beam steering device which is one dimensional and has a substantially parabolic grating profile. The problem with having a parabolic grating profile is that in order to steer a beam into higher diffraction orders, the resulting parabolic grating profile must be deep. This deep profile is both difficult to fabricate and has high losses in diffraction efficiency. An alternative to the microlens and the phase grating designs is the phased array-like design of the present invention.
The invention disclosed herein is a device for agile steering a laser beam using a pair of complementary optics elements which have a phased array-like profile. The phased array-like profile consists of pixelated steps of varying depth, with no step introducing a phase delay of more than one wave. The structure of the present invention can steer a laser beam by translating one element with respect to the other by a distance that is an integer multiple of the step width. The diffraction efficiency of the phased array-like design is a sinc2 function of the steering angle and the sidelobes are weak in the immediate vicinity of the steered beam, while any strong sidelobes are well separated from the target order.
The phased array-like design of the invention can be fabricated using general binary optics technology. For example, binary optics elements with the phased array-like design were fabricated using a 4 mask process with a minimum feature size of 5 xcexcm. The device demonstrated agile steering of a 1 cm diameter green HeNe (xcex=0.543 xcexcm) laser beam over a 6 degree field of view.